Erik Weaver

paul wheaton wrote:Last night I watched DVD1 as one big chunk ....   it was missing a small piece.  

Unfortunately, I made two pages of notes of things that needed to be changed/mended and then we need to look again.  So it might still be another day or two.

I for one, am glad you are going through them again, as a finished presentation, looking for errors and omissions. We've waited this long, a little while longer to help ensure completeness and quality is well worth it!

4 DVDs vs. 8 DVDs.

A point of confusion may be whether there are only 4 DVDs, as appears to be the case, and was the original idea in the kickstarter. Thus the 8-DVD set would NOT include 8 different DVDs, but rather two sets of the same 4-DVD set.

Charles Deshler wrote:Really excited to get this coming. I just finished my new shop this week and i am ready for a Rocket stove to heat with. Does anybody know what the clearance is to walls/wood floor?

It depends upon how you design the build. Are you going to use heat shielding or not? I know Ernie and Erica discuss this in their new book, "The Rocket Mass Heater" so you may wish to get a copy of that. It is also discussed in various threads, which are free but require your time to be spent in greater amounts than reading their book. You may also look to your local building codes, and the ASTM standards for masonry heaters. A RMH is a hybrid of a masonry heater and a standard wood heater: the masonry standards apply to the thermal mass (bench, bell, etc); and the wood heater standards apply to the metal barrel.

Off the top of m head, which means I may be mistaken these are nominally a 3 to 4 foot clearance from the barrel, and half that distance if properly heat shielded, and as little as 4-inches for the mass, provided the proper thickness of mass is in place (a minimum of 8-inches as I recall). So if you are able to provide 4-foot clearance all the way around, I doubt you need to worry (this includes to the ceiling, which to my mind is certainly one of the more critical concerns: heat rises, after all). Anything less, and you need to take a careful look at your design parameters.

Not so much a specific answer, as it is a procedural answer ...which I think is best, not knowing what design you plan to build.

And always take extra precautions with the exit flue/chimney. Observe best building practices here, all the way around, paying extra attention to through-wall/ceiling and height of the chimney (insulated or multiple walled pipe is recommended in most cases, and may be required by your code - you won't know until you look at your local building codes). My opinion is that it is best to purchase pre-fab pieces for the through wall/ceiling and outdoor chimney - basically all the flue/chimney elements once they exit your RMH. And pay attention to the clearances.

Assuming you build the RMH as it is described in the literature found on this forum, on Donkey's forum, and in the few recommended books (again, Ernie and Erica's new book is probably the single best resource on that point now), the most dangerous elements are going to be how you exit the exhaust. I recommend being conservative in this area, whether you have local building codes or not, I would strongly recommend observing best building practices for your exhaust.

On a personal note, given how inexpensive temperature probes and thermometers are, I would plan to build several of these into your RMH at critical heat areas, so that you may observe these critical temperatures during operation.

Peter van den Berg wrote:

F Styles wrote:holy goodness 1800 degrees F? are you kidding me? For real are you really getting 1800 inside your system?

That level of heat isn't uncommon in rocket heaters. In my own batch box design the highest recorded temperature has been 1180 degrees Celsius which converts to 2160 Fahrenheit. At the time, I wasn't even sure whether or not I was recording the hottest spot. Exit temperatures at the top of the riser are routinely over 900 C or 1650 F. So Sky is right, he really need to keep down those freaky temperatures inside the core or the whole thing would corrode like mad in no time. Whether or not a gas analizer would be satisfied about the results since the temps aren't really up to the phisical limit remains an open question.

Yes, quite common temperatures. My prototype that I tested the last two winters (a basic nominal 6" j-style barrel RMH) commonly burned between 1400 (that's really quite "cold") to nearly 2000 *F (1960-1980 *F ranges, spot checked, not continuous monitoring) at the top of the entry point going into the burn tunnel from the feed tube. The hottest part should be found deeper in the burn tunnel, at the bottom of the fire riser as I recall, but I never measured that point.

But as far as testing heat output, why melt aluminum, just buy a digital thermometer and appropriate test probes. I bought a decent digital unit for $18 on Amazon and a variety of probes, ranging from 200 *C or so on the low end (for measuring heat penetration of the thermal mass and under the burn tunnel to verify I wasn't transferring too much heat to the floor) and up to something like 1000-1200 *C or so (I don't recall of hand) for measuring the hotter areas. That's not sufficient to get at the hottest areas, but it is usable for measuring the transition from feed tube to burn tunnel.

Another test option is to purchase a variety of test cones, as are used to test kilns.

I prefer the digital probes, but then again I'm really only doing it for my own testing, and these days you can buy very accurate (within a 1%-2% as I recall) devices. If one wanted to get all fancy, the digital thermometer could be rewired to run on electric a.c. plug-in (or simply hooked to a comparatively masses storage d.c. battery) and feed the read out into an old dedicated computer and log the data for the entire burning season. I doubt I'll do that, but it wouldn't be all that difficult. If anyone wants to go that route, there are also basic home weather stations that can be bought for a few hundred dollars and that could supply a decent number of environmental data points (and connected to various online weather station collection systems, if one also wishes to become a home weather station data point for others).

Socrates Raramuri wrote:Sand?
I thought about this, as well, and watching one video it was mentioned that someone used sand as part of the mass but that this was inappropriate because sand insulates... So there ya go, i thought.
Would it be the best insulator? Probably not. But it's everywhere and free. And often 'the best' can be substituted by simply applying more of what might seem an inferior product.

Technically, it is the multitude of tiny air gaps between the sand that insulate

Sand mixed with clay, for example, is not at all insulative, but rather adds structural support to the clay, helps it not to crack so much, etc.

But if you fill a bench with sand, yes, that is going to insulate to a reasonable degree because of all the air pockets that are trapped between the particles of sand, and *air* is a very good insulator.

So I say go for it! Just use more of it.

Minor Update.

As I write this, it is July 2015, and obviously the winter heating season 2014/15 has ended. I never resumed the use of my flue damper. And I never noticed any trouble with just placing the fire bricks over the opening of my j-style rocket heater. I just kept closing the opening more and more, to 1.25 inch while the coals were dying down (the width of one fire brick split), and then just about an 1/8-inch or so open when I went to bed or to work. My thinking was this was enough to permit gases to escape, should any be present.

Other days, when the wind was from the "wrong" direction (I never got around to increasing the height of my chimney pipe, given this was a temporary and prototype build) I covered the feed tube opening first with a piece of heavy aluminum foil (still flexible, still for cooking use, just the heavy foil, not the very easily torn thin foil), then on top of the foil a couple of 12x12 inch floor tiles I had left over (which completely covered my feed tube opening), and then on top of the tiles, setting the three split fire bricks I used to moderate my feed tube opening when burning.

I cannot say that I ever detected a cold breeze flowing into the house using this set up. Thus, as of now, I am not convinced loss of heat is of great concern. Granted, I also did not simply allow a full 6-inch opening to remain fully open through my wall all winter either! But my opinion is that closing one end of a loop (feed tube, to barrel, to chimney pipe) is adequate to slow or halt the loss of indoor air to the atmosphere, to any appreciable degree.

I imagine a bottle, and trying to blow smoke into it, simulating a cold winter wind. How effectively does the smoke enter the bottle? How deeply? I am thinking, not so much. I'm not saying using a flue damper might not be a good idea; but my opinion is that it ought to be located in an obvious location, so that one remembers to *open* it before starting the new fire hehehe, having forgotten once or twice ...I can say the fire tends to draw much better when the damper is open

Now, bear in mind that I live in an older house and I *do* have old windows and doors, so I already have "heat leakage" in the house; this is *not* anything like a super-tight house.

If I understand your question, I'd say the answer is a qualified yes.

Whether there is a limit to how large the space between the fire riser (that is what the insulated vertical element of the j-tube is normally called) and the outer barrel (or welded up plate in your example), I do not know. I suspect not within reason; but what is "reasonable" is then the question. Think in terms of bell masonry heater design. So long as the containment area of the bell is less than that which will cause all the heat to be sucked out and vapor to condensate before rising out of the heater (through the chimney, into the atmosphere), it will work (assuming a properly designed and installed chimney is in place, and other factors that constitute a good draft, pulling the exhaust out of the house).

The next question, is why?

Why would you *not* wish to benefit by having thermal storage of the heat? It is this which moderates the heat released into the room. Without substantial thermal mass, the rocket heater works a lot like a wood burning stove: hot when burning and cold when not burning. The difference is the rocket heater burns through the wood much more quickly than a wood burning stove. For many reasons this is a very good thing; however, one reason this is *not* a good thing, is unless you have thermal mass to capture and slowly release all that fire energy (heat) it is less comfortable as a heat source, and requires being burned more often, and when burning requires more attention than a common wood burning stove (Peterburg's batch box eliminates that headache, but cannot alter the physics of high heat production without thermal mass to capture and then slowly release that heat: a high rate of energy production is only half the system; capturing and slowly releasing that heat is the other half of the system).

I burned a test rocket stove/heater this past winter. I was primarily concerned with testing the basic build and operation (how I feel living with my dragon, as it were). Since I also built this on my carpeted living room floor, above a basement which I did not add support joist under, I did *not* add thermal mass (too heavy). The result is the barrel got the place pretty darn warm, and even hot at times (roughly a 1350 sq.ft. upstairs and 1200 or so in the basement; it did not heat the basement at all, so far as I could tell: heat rises, after all). It was nice when burning, in terms of heat output. And the things in the living room warmed to some degree, I'm sure, but nothing like a proper thermal mass would. As a result, temperatures began to drop as soon as the fire stopped burning. So I would run the temps up to 80 degrees F or more, and then cover up under my electric blanket whilst temps fell back to 50 F or so, and then either go to bed or start the heat/cooling cycle over again.

I still saved a lot of propane. So it was worth the trouble, in terms of money saved. I may have even paid for the supplies I bought to build the prototype (I'd have to check my records to be certain of that; if I didn't pay for them outright, I paid for a lot of the materials in saved propane costs). But I also learned a number of other things. Namely, for *me* the batch box is a better design, because I'd rather read a book than get up every 5 or 10 minutes to tend the j-style feed. And I really, really do need to add thermal mass; for me that has always been the plan, and this years build will accommodate that; but had I been doubtful of the benefit of thermal mass to capture that heat and slowly release it into the room over a period of hours, instead of minutes, I'm convinced I'd consider the thermal mass to be a good investment, both in efficiency and comfort.

There are all kinds of ways of making thermal mass look nice. I would not give up on that easily (in fact, I would not give up on that at all). I certainly recommend planning on adding thermal mass, be that bells, benches, or a design that has the appearance of a more traditional masonry heater. There are many beautiful designs, so it is hard for me to imagine not finding something you would enjoy living with.

That's my 2-cents. Add a couple buck and you can buy a cup of coffee

I think I would look up building standards for masonry stoves. I don't recall the ASTM-E1602 specifically mentioning this. However, if you build according to that standard, I should expect you'll be fine. The long and short of that, in terms of what may be applicable, I would say is to make sure your stove thermal mass is a minimum of 8-inches from your other walls. Personally, I would also isolate your stove mass with insulation from the rest of your house, unless that is already isolated with insulation from the earth.

I've not used one.

It is a cook stove, not a heater for warmth. As a cook stove I suppose it might last as they claim. Cooking is of short duration, so maybe it'll hold up. But 10-years? That's a lot of cooking at 2000 F in the fire box.

I certainly would not expect it to hold up as a heater (which it is not being sold as, to be fair). 2,000+ F for such extended times, I would expect the metal to break down. But others who have actually used metal will be a better source than I am. I just know I've read of enough metal failures, I'm not going to waste my time even trying it for heat; I might for cooking, if I can get the metal cheap.

Antony Felton wrote:Hi all, thanks for the input, the burn tunnel has been shortened and works, the smaller this thing is the better for my situation. I will also lift the quartz slab (sorry still waiting to find out the specs.), with 4x2 plywood strips. As for the bell i going with the old school 200l drum, but a 50mm would or feels like it would be optimal. I will post an update on the reorganized design.
Ta ta for now Antz

If you are trying to lift the quartz to provide air flow (a very good idea in my opinion) I would consider using square steel tubing instead of a wood product (especially one which is impressed with chemicals you may not like off gassing into your living space). I've seen test lab builds online that have done this to protect their floors during test runs. I suspect it would work very well in your case too; better and safer than a flammable product in my opinion.

I would get a minimum of 1" square tubing. That should provide adequate air flow. More space = more peace of mind, perhaps, but costs increase too. I don't think anything more than 2-inch square tubing would be needed. On concrete I'd go with 1" and sleep well; on a wooden floor, trailer, etc, I may sleep better with the 2" air gap. Just my opinion.